In the telecommunications field, particularly in long distance networks, long distance network providers continually strive to increase the traffic carrying capability of their transmission medium. For example, since fiber optic cables have increased bandwidth over known twisted pair or copper wire cables, fiber optic cables are used increasingly for connecting network stations and other network elements. As a result, a greater number of stations or network elements can be connected over a fewer number of fiber optic cables, as opposed to prior cables. In other words, each fiber optic cable can handle numerous trunks, as opposed to prior cables.
Unfortunately, if one or more of the fiber optic cables fail, massive disruption of services to a large number of network customers and users can result. Network service providers or telecommunications carriers therefore strive to quickly and economically restore traffic effected by these disruptions or "outages." Restoring network outages generally requires four steps: (1) detecting the network failure, (2) isolating the location of the failure in the network, (3) determining a traffic restoral route, and (4) implementing the restoral route. Network restoration must be executed quickly to ensure minimal interruption of network traffic. Therefore, nearly all telecommunications carriers wish to restore traffic within a few seconds or less. The telecommunications carriers typically restore the highest priority network elements first, and as many of such elements as possible within a short period of time.
Currently, telecommunications carriers simulate possible failures and determine restoral routes to develop a "pre-plan" by collecting large amounts of data reflecting the logical topology of the network. The collected data is often retrieved from network engineering databases which reflect the logical construction of the network, such as indicating the connections and paths of all network traffic trunks. An engineer or network analyst analyses the collected data, compares the collected data to the geographic or physical layout location of the network, and then generates the pre-plans therefrom. Since the pre-plans are developed prior to any failure in the network, when a failure does occur, a plan already exists for restoring traffic affected by the failure. In general, a pre-plan corresponds to a segment of the network that can incur a failure. If that segment fails, then the corresponding pre-plan is retrieved, and its restoral route implemented.
To determine where in the network a failure has occurred, a central location often receives various alarms from the network, which are generated in response to the failure. Numerous algorithms are performed by a central computer to apply or correlate the various alarms to each corresponding trunk in the trunk topology. The computer or analyst must then match the alarms to a physical network topology to isolate the location of the failure within the network, typically within a segment of a trunk between two nodes. In sum, existing methods of isolating a network failure include the steps of: (1) receiving numerous alarms from nodes throughout the network; (2) collecting logical topology data for each trunk generating each alarm; (3) applying each received alarm to the logical topology data for each trunk; (4) determining a failed span for each failed trunk, where the failed span can be larger or smaller than the actual physical span of the trunk, depending on the nodes on which the trunk is patched or routed: and (5) combining all determined failed spans and correlating the spans to determine a physical location or span of the failures.
Each node traversed by a failed trunk produces an alarm. Often, multiple trunks fail as a given optic cable fails. Since each trunk in the network typically traverses multiple nodes, the network typically produces numerous alarms from multiple nodes as a result of a failure. Each alarm must be correlated with the logical trunk topology to isolate the failure of a given trunk to a segment between two of the multiple nodes that issued alarms. This is the maximum granularity with which the failure can be isolated. Extensive processing, and thus time, is required to isolate a failure in the network because of the numerous alarms, trunks and nodes in a network. The processing and time also increase as the size of telecommunications networks increases. As noted above, telecommunications carriers wish to restore traffic within a few seconds or less, and thus such delays required to isolate a failure are undesirable. Additionally, if only a few trunks fail, the network may provide an insufficient number of alarms from which to isolate the actual physical span in which the failure occurs.
After isolating the failure, the analyst can then identify the appropriate pre-plan. For example, by isolating the failure on a physical map of the network, the analyst can then identify an alternative route that restores all failed traffic, without sacrificing other traffic or creating new outages. Isolating a failure within the network requires extensive processing, particularly with large networks. Again, such extensive processing necessarily requires processing time, and therefore increases the delay in restoring the network following the failure.